This invention relates to a drainage channel with means for maintaining proper slope during installation of the channel, and a method for installing a drainage channel in concrete. Drainage channels of the type referred to in this application are open top drainage channels which are used to drain parking lots, airports and driveways, as well as various interior fluid drainage applications. Usually a longitudinally extending grate is set into the open top of the drainage channel. Both the channel itself and the grate may be constructed of various materials and according to various processes to support light, medium or heavy loads. In the particular embodiment discussed in this application, the drainage channels are cast of "polyester concrete", a concrete aggregate material containing quartz and inert mineral fillers bonded with polyester resin.
Typically, the drainage channel is cast in relatively short lengths of one meter. Each channel has a predetermined depth and a bottom slope, for example, 0.6%, from one end to the other. A drainage channel is formed by using cast channel segments having successively higher walls so that when put in the proper order in a trench they collectively form a run having a pre-determined slope as described above.
The top opening of the channel is usually covered with a grating and is flush with or very slightly below the surface to be drained. The channel segments are embedded in concrete within a trench which must be properly prepared to receive the channel segments in proper order and with proper slope. Usually, the trench must be relatively level relative to the surface to be drained and properly graded with a level string line.
Even if the trench is properly excavated, the channels must be correctly placed and secured in the trench. This is difficult because the channel must rest on a bed of concrete or some similar bonding agent. Heretofore, difficulty has been experienced in properly placing the channels within the trench and maintaining their proper position until the concrete hardens. This is because the channels are naturally buoyant. If the channels were placed in a trench and concrete poured around the channel all the way up to the top opening of the channel, it would float upwardly from its proper position. This occurs because each channel has a central void which accounts for a substantial percentage of its volume, but not its weight. The channel, whether wholly or partially immersed in unset concrete (which acts as a fluid) undergoes a loss in weight equal to the weight of the fluid it displaces. The channel therefore tends to rise to the depth in the unset concrete so that the displaced volume to concrete weighs the same as the entire channel. If this buoyancy is permitted to alter the slope of the channel segments, the drainage channel drains either poorly or not at all. Heretofore, this problem has been solved first by placing a layer of "grout", such as very thick concrete, in the bottom of the trench. The channels are then laid on the grout layer and grout is either taken away or added until the channels are properly leveled with a string line. Then, concrete is poured up to and just over an enlarged, outwardly extending base on the channel and allowed to harden overnight. The hardened concrete acts as an anchor which secures the channel into the trench. Then, the next day, the remainder of the concrete is poured into the trench up to the level of the top opening of the channel. This concrete is allowed to harden whereupon the process is complete. This process is slow, expensive and requires considerable skill. Furthermore, adjustments must be made by removing or adding grout to the grout layer on which the channel is resting. This requires that channel segments be removed to get at the grout layer.
Furthermore, the separate placement of the grout layer, the first pour, and the second pour of concrete results in a fragmented structure within which the drainage channel is encased. A fine crack is left between the first pour of concrete and the second pour which remains even after all the concrete has hardened and cured. This is a potential source of leakage of ground water into the structure which over a period of time can cause deterioration of the drainage system, especially if it is subject to freezing.